RK-287107 is a potent TNKS/TNKS2 inhibitor (IC50 = 14.4 nM) with >7000-fold selectivity against the PARP1 enzyme, which inhibits WNT-responsive TCF reporter activity and proliferation of human colorectal cancer cell line COLO-320DM. RK-287107 also demonstrated dose-dependent tumor growth inhibition in a mouse xenograft model. RK-287107 is a promising lead compound for the development of novel tankyrase inhibitors as anticancer agents.